This Shared Instrumentation Grant Application is for funds to purchase a flow cytometer for the core flow cytometry laboratory at Dartmouth Medical School. The core laboratory has successfully and effectively utilized an Ortho 50HH Cytofluorograf for eight years, and has established a major user group of 12 principal investigators from the Departments of Biochemistry, Medicine, Microbiology, Pharmacology and Toxicology, and Physiology. The flow cytometry laboratory has been, and will continue to be administered as a shared facility of the Norris Cotton Cancer Center. An advisory committee establishes fees and guidelines for use of the facility, and assists in the setting of priorities. A faculty member directs the facility, which is staffed by one full-time and two part-time technologists. Markedly decreased reliability (increased down-time), technical limitations of the 8-year old instrument, and ineffective technical support from the manufacturer make it essential to replace the existing flow cytometer, which is pivotal to projects funded by a large number of NIH grants.